1. Field of the Invention
The invention relates to distribution of digital content.
2. Related Art
Distribution of digital content for media streams, such as for example movies, is subject to several problems. One problem is that it is easy to make exact copies of digital content, thus allowing any recipient of that content to redistribute it, whether or not authorized to do so. It would be advantageous to be able to distribute digital content, particularly digital content for media streams, without fear of its unauthorized distribution. This would be particularly advantageous when it is desired to distribute digital content using a communication link, such as for example a computer network or other technique for distribution to end viewers (for example, either on demand, in anticipation of future demand, or in response to something else).
One known solution is to mark the digital content with a “fingerprint,” so that an unauthorized redistributor of the content can be identified, thus hopefully deterring potential unauthorized redistributors. However, fingerprinting of digital content is subject to several known problems, including (1) that presentation of the media stream might be degraded by altering the original content, (2) that recipients might attack the fingerprint, either by altering it or erasing it, or (3) that it might be difficult to determine the unauthorized redistributor with sufficient certainty, particularly if multiple unauthorized redistributors collude to make copies in which the fingerprint has been altered or erased using information available to those multiple recipients.
Another problem is that the fingerprint might interfere with distribution, decoding, or presentation of the original media stream. In particular, when the original media stream is encoded using a known format for movies, such as for example the MPEG-2 format, the amount of data included in even a single movie can be quite large. It would be advantageous for any fingerprinting method to retain the structure of the original MPEG encoding (including packetization of the original media stream), so that the particular fingerprinted digital content is not changed for distribution purposes by the fingerprint. In particular, it would be advantageous to assure that (1) the length of the fingerprinted digital content is the same as the length of the original digital content, and (2) sending the fingerprinted digital content can be interrupted and restarted, such as when using network communication techniques, without having to recompute the fingerprinted digital content and without having to maintain large amounts of intermediate state information about the fingerprinted digital content.